1. Field of the Invention
The present invention relates to a method for the manufacture of a foil capacitor, cut out into unit blocks from a capacitive strip made by the stacking or coiling of metallized dielectric films.
2. Discussion of the Background
The manufacture of foil capacitors out of metallized dielectric films is known. Generally, plastic films are used, comprising a metallized zone and a non-metallized side margin. Two films are superimposed, their non-metallized side margins being on opposite sides in order to obtain a pair of films constituted by an even-order film and an odd-order film. At least one pair of metallized films is wound in a determined number of turns around a large-diameter wheel. There is thus obtained a capacitive strip, known as a parent capacitor, comprising alternating even-order and odd-order layers. Then, each of the flanks of the capacitive strip is covered with a metal (or alloy) in order to make output plates. Each output plate enables the same-order layers to be connected to one another mechanically and electrically. This operation, which is done by the spraying of molten metal, is known as Schooping or Schoop's metal spraying process. The process is completed by cutting the capacitive strip out into unit blocks which are generally parallelepiped shaped. Then the connection strands are soldered, if necessary, to the output plates and, optionally, the capacitor is covered with a protective coating, made of epoxy resin for example.
This operation of cutting out into unit blocks is always difficult in view of the small thickness of the metallized films (some microns) and sometimes leads to surface deterioration of the cut sides of the blocks.
The cutting out is done with a circular saw blade rotating about an axis that passes through its center. Its diameter is far greater than the thickness of the capacitive strip to be cut. The saw blade engages and penetrates the capacitive strip transversally, i.e. substantially perpendicularly to the plates. The rotational axis of the saw blade is located substantially in the median plane of the capacitive strip.
When they are damaged, the cut flanks of the blocks may be the site of short-circuits between an even-order layer and an odd-order layer. These short-circuits are created by the splinters or chips that are cut free by the teeth of the saw blade. This process of the cutting free of splinters harms the cut surface. The short-circuits damage the electrical properties of the capacitor which may even become unusable.